28.2 Life in the Solar System28.2 Life in the Solar System

Life as we know it…Life as we know it…

Carbon-basedCarbon-based

Originated in a liquid water environmentOriginated in a liquid water environment

The Moon and MercuryThe Moon and Mercury

LackLack– Liquid waterLiquid water– Protective atmospheresProtective atmospheres– Magnetic fieldsMagnetic fields

So these bodies receive too much UV So these bodies receive too much UV radiation, the solar wind, meteoroids and radiation, the solar wind, meteoroids and cosmic rayscosmic rays

VenusVenus

Too much atmosphere!Too much atmosphere!

Its atmosphere is too dense, dry, Its atmosphere is too dense, dry, scorching, hotscorching, hot

Jovian PlanetsJovian Planets

Do not have a solid surfaceDo not have a solid surface

Some researchers think that life could Some researchers think that life could have evolved in their atmosphereshave evolved in their atmospheres

Pluto and the Jovian moonsPluto and the Jovian moons

Most are too coldMost are too cold

Jupiter’s moon Europa may have liquid Jupiter’s moon Europa may have liquid water beneath its frozen surfacewater beneath its frozen surface

Saturn’s moon Titan has an atmosphere of Saturn’s moon Titan has an atmosphere of methane, ammonia and may have liquid methane, ammonia and may have liquid water – but it may be too coldwater – but it may be too cold

Europa’s surfaceEuropa’s surface

Enceladus – moon of Saturn, with Enceladus – moon of Saturn, with water geysers water geysers

MarsMars

Probably the planet most likely to harbor Probably the planet most likely to harbor lifelife

Water is scarce, but presentWater is scarce, but present

The atmosphere is thinThe atmosphere is thin

No magnetism or ozone layerNo magnetism or ozone layer

Atmosphere was thicker and planet was Atmosphere was thicker and planet was warmer in the pastwarmer in the past

Water on MarsWater on Mars

The The Viking and Mars GlobalViking and Mars Global Surveyor Surveyor show photographic evidence of flowing show photographic evidence of flowing and standing water.and standing water.

In 2004, the European In 2004, the European Mars ExpressMars Express confirmed ice (water) at the poles.confirmed ice (water) at the poles.

OpportunityOpportunity found evidence that water found evidence that water used to be very abundant.used to be very abundant.

Evidence of water on MarsEvidence of water on Mars

The “Face” on MarsThe “Face” on Mars

Life on Mars?Life on Mars?

Even with the water and atmosphere and Even with the water and atmosphere and all of the probes that have been to Mars, all of the probes that have been to Mars, no life or fossils of life have been found.no life or fossils of life have been found.VikingViking robots tested Martian soil for robots tested Martian soil for bacteria and other life.bacteria and other life.However, the orbiters have not widely However, the orbiters have not widely surveyed the area. surveyed the area. Particularly, they have not surveyed the Particularly, they have not surveyed the area near the polar ice caps.area near the polar ice caps.

What do scientists think about Mars What do scientists think about Mars today?today?

Biologists and chemists agree that no life Biologists and chemists agree that no life exists on Mars today. exists on Mars today.

We will need to explore Mars more to We will need to explore Mars more to learn if life existed there in the past.learn if life existed there in the past.

Alternative BiochemistryAlternative Biochemistry

Would we necessarily recognize life if we Would we necessarily recognize life if we saw it?saw it?

Could it be different from life as we know Could it be different from life as we know it?it?

Some scientists think that silicon might Some scientists think that silicon might replace carbon in other lifeforms.replace carbon in other lifeforms.

However, its bonds are weaker.However, its bonds are weaker.

Maybe ammonia is used in place of water.Maybe ammonia is used in place of water.

Alternative BiochemistryAlternative Biochemistry

You would have to have lower You would have to have lower temperatures for ammonia to remain a temperatures for ammonia to remain a liquid.liquid.

Colder temperatures are a problem.Colder temperatures are a problem.

There would not be enough energy to There would not be enough energy to drive biological processes.drive biological processes.